Glass is installed in the front surface of a display device, such as an LCD or an LED, in portable terminals including smart phones which recently come into use. Furthermore, a specific function is designed to be executed by touching front glass because a touch pad function is included in such a display device. Furthermore, such front glass is also widely applied to home appliances, such as TV, and an electronic device for vehicle, such as a navigator, in addition to a smart phone and a personal terminal having a specific function. Furthermore, such front glass is also called touch window glass in a device having a touch pad function, such as that in a smart phone.
Such front glass is applied to products as 2D glass commonly having a plane shape. Recently, the front glass of TV, that is, one of home appliances, is generally formed into a curved surface or the ends of front glass on the left and right sides are formed into curved surfaces on the basis of a single axis. The front glass of a smart phone is also formed of curved surface glass having various types. Furthermore, glass formed to have a curved surface as described above is commonly called 3D glass.
Furthermore, for example, the 3D glass of a smart phone may be formed into a curved surface with respect to any one of an X axis and a Y axis on the XY plane. Furthermore, although the 3D glass is formed to have curved surfaces with respect to a single axis as described above, the entire front glass may be formed into a curved surface or at least one of the left and right ends of front glass may be formed into a curved surface. Furthermore, some of four sides forming front glass may be formed into curved surfaces, or all of the four sides may be formed into curved surfaces.
As shown in FIG. 1, 3D glass having a curved surface as described above is commonly formed by an upper mold Da and a lower mold Db. That is, the shape of the 3D glass is determined by the shape of a cavity formed between the upper mold Da and the lower mold Db. That is, in the state in which glass of a plane shape initially indicated by Ga has been heated, the glass is deformed by weight of the upper mold and formed into front glass having a 3D shape, such as that indicated by Gb.
That is, when 3D glass is formed, in the state in which glass, that is, a material, has been heated up to a temperature at which the glass may be subjected to plastic deformation by an external force, 3D glass (also called curved glass) having a required shape is completed by applying pressure using the upper mold and the lower mold. Such a processing temperature is very lower than a melting point, and pressure through the mold is applied to glass.
In this case, the glass is processed in the state in which it has been heated up to a temperature at which the glass may be subjected to plastic deformation by an external force. Furthermore, the mold which is used to form glass is made of graphite. It has been known that mirror-like processing is substantially impossible for such graphite. Accordingly, when a specific force is applied to front glass through the mold in a high temperature atmosphere, a pattern or shape on a surface of the mold is inevitably delivered to touch window glass.
In particular, in the curved surface portions of the front glass, pressure higher than pressure in a plane portion is delivered from the mold to glass, thereby substantially greatly deforming the glass. Accordingly, a disadvantage is generated on a surface of the glass because the processed surface of the glass moves along a surface of the mold in a fixed state. As described above, 3D glass inputted between the upper mold and the lower mold and produced through the surface contact of the entire surface of 3D with the mold may include a disadvantage, such as a fine scar or mark, in a curved surface portion compared to a mirror surface.